This invention relates to para-ordered aromatic heterocyclic graft polymers and copolymers.
In general, the class of aromatic heterocyclic extended chain polymers are well known for their outstanding thermal, physical and chemical properties. Considerable research has been directed toward using poly(p-phenylene benzobisazole) polymers as the reinforcing elements in polymeric composites. These polymers, also known as rigid-rod polymers, have a high modulus and high strength, and can act as reinforcing elements similar to the reinforcement afforded by chopped fibers, but with the reinforcement taking place at the molecular level. Unfortunately, these polymers are essentially non-melting and have proven difficult to economically process into articles. In order to fashion such polymers into articles of commerce, for example, fibers, films, fibrids, and the like, it is necessary that they be in solution or dope form. Although such polymers can be dissolved in various acidic solvents, such as sulfuric acid (SA), methanesulfonic acid (MSA), chlorosulfonic acid (CSA), polyphosphoric acid (PPA), and the like, difficulty is often experienced in preparing and using the polymer-acid compositions or dopes because of poor polymer-acid solubility.
Normally, a precipitated or dried particulate form of the polymer is dissolved in a strong acidic solvent by mixing the polymer particles at elevated temperature for a period of several hours to several days. The resulting dopes often contain undissolved polymer and must be filtered before further processing into articles.
Considerable research has been directed toward using poly(p-phenylene benzobisazole) polymers as the reinforcing elements in polymeric composites. These polymers, also known as rigid-rod polymers, have a high modulus and high strength, and can act as reinforcing elements similar to the reinforcement afforded by chopped fibers, but with the reinforcement taking place at the molecular level.
Development of these polymers for applications requiring bulk forms has been hindered by the difficult processibility of these polymers due to their limited solubility and complete infusibility. Previous attempts to improve polymer solubility or fusibility through modification of the polymer structures such as by the inclusion of diphenoxybenzene "swivels" or points of articulation to form articulated rod-like polymers have not been satisfactory. Processing difficulties have been somewhat circumvented by novel processing concepts and approaches such as molecular composites in which the rod-like polymer is uniformly dispersed at the molecular level in a fusible, malleable host or matrix. Implementation of this concept has previously entailed novel synthetic approaches, including the preparation of poly(p-phenylenebenzobisimidazole) structures with polypropylene side-chains. Although these copolymers could be readily processed neat at moderate temperatures and pressures to give consolidated bulk forms with good mechanical properties, they exhibited limited thermooxidative stability.
Accordingly, it is an object of the present invention to provide rigid-rod heterocyclic polymers which are fusible.
Other objects and advantages of the present invention will be apparent to those skilled in the art from a reading of the following detailed description of the invention.